The present invention relates to a pneumatic tire more particularly an improved tread portion.
In recent years, the so called studless tires are widely used in various vehicles not only passenger cars but also heavy duty vehicles such as trucks and buses. In such studless tires, block type tread patterns are usually employed to improve road grip (snow grip, ice grip). In the heavy duty vehicles, however, due to the extremely heavy load in comparison with the passenger cars, the steering stability is liable to decrease because blocks are lower in the rigidity than a rib which is usually employed in summer tires. Notwithstanding, it is necessary for obtaining a necessary minimum road grip that the block tire is further provided with sipes to utilize the edges thereof. Such sipes are shown in FIGS. 7 and 19. The sipes divide the blocks into small parts, and the sipes open when the blocks are subjected to a circumferential force. Accordingly, the block rigidity decreases and the steering stability decreases. Further, uneven wear so called heel and toe wear occurs, and sometimes cracks and tear-off occur.